In installations for the continuous production of foam blocks or foam sandwich panels, it is known to transport a bottom foil or lower surface layer on a conveyor belt and then apply a foamable reaction mixture to it. The applicator device used for this purpose generally consists of a mixing head which reciprocates transversely to the direction of movement of the conveyor belt so as to effect linear distribution of the reaction mixture. Accumulation of reaction mixture occurs at the turning points of the mixing head because at these points the mixture is thrown against the upturned sides of the bottom foil and then runs down them. This causes overlapping of mixture with the formation of superimposed layers in the finished foam and an irregular surface.
It has been proposed to arrange an inclined plane and overflow container upstream of the conveyor belt used in block foaming installations, and to apply the reaction mixture to the bottom of this container. The overflow container is designed so that the reaction mixture contained in it already begins to react as it moves upwards in the container so that when it flows over to the inclined plane it is already in the process of developing into a foam block. Characteristic of these processes are those disclosed in U.S. Pat. Nos. 3,786,122 and 3,832,099.
One disadvantage of this apparatus is that gas bubbles enclosed in the reaction mixture can no longer escape from the surface because the already partly reacted foam on the surface is so tough that air bubbles can not penetrate it. The bubbles therefore remain inside the block as troublesome defects. The formation of such gas bubbles is unavoidable because gas is already dissolved in the reactants and escapes during the mixing process due to the release of pressure at the constrictions in the feed pipes (e.g. nozzles) and then collects to form larger bubbles in the reaction mixture.
It is an object of the present invention to provide a process and an apparatus whereby mixture can be applied more uniformly to the moving support and at the same time a bubble-free foam can be produced.